The best method to view the performance of a moveable light is to enable Frustums on a directional light. You will see that the frustum encompasses and calculates for all moveable objects in a scene. It recalculates the lighting for every frame, altering the light and shadow maps as necessary. This is why moveable lights are the most cost heavy lighting. A key consideration is also that the attenuation range alters the costliness of the light. A smaller attenuation cone or sphere will be less costly than a larger one.

Smaller attenuation range (cone) requires less performance.

Larger attenuation area (compared to left) has greater performance cost.

When To Use

• If you want to do a fully dynamic sun cycle, stationary lighting will not work because the shadows are baked and you also need to move the sunlight.
• Lighting that highlights a moving character or actor (e.g., lighting moving along a rail).

If you only want to alter the intensity or color of a light, then you should use a stationary light as it is less costly and achieves the same goal.